Passive House goes to work

by sadia_badhon | May 27, 2020 10:29 am

By Graeme Verhulst, Architect AIBC, MRAIC, CPHD

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The benefits of high-performance buildings are being recognized by owners, designers, and policy-makers alike. This led to an uptake in Passive House (PH) design, as it is widely recognized as the most rigorous energy-based standard in the construction industry today. It is a proven way to ensure the best possible comfort and air quality along with low operation and maintenance costs.

The standard has so far been almost entirely applied to residential buildings in North America. Located in Greater Victoria, British Columbia, the Charter Telecom headquarters is poised to become the first commercial office building in North America to earn PH certification.

Achieving a high-performance building status requires a design co-ordinated across a web of interconnected factors. It may sound complicated, but is doable with good planning and intention. This case study demonstrates a net-zero energy ready (NZER) commercial building can be constructed on a challenging site by trades without the requisite training, and sans the need for financial incentives or grants, at a reasonable cost.

Owner’s motivation

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When developing a new, roughly 1500-m² (16,000-sf) office building to house its growing staff, Charter Telecom enumerated several priorities including:

• the facility must be representative of Charter’s brand as an innovative and forward-thinking company;
• improve the already vibrant staff culture and help recruit the best and brightest in the industry;
• the building was to act as a sales tool—a physical demonstration of what Charter does well;
• set a new standard for the changes coming to the neighbourhood; and
• low-operating expenses and reasonable construction costs.

By the end of the schematic design process, Charter was willing to embrace two non-traditional approaches that are still in their infancy in Canada—the Passive House standard and engineered mass timber construction. Both these approaches were made challenging by site restrictions, which quickly became the main driver of design.

Design process and challenges: site and massing

With PH certification identified as a core goal, one of the first considerations was massing and orientation. The site is narrow, with the long direction oriented 19 degrees off the north-south axis. The road frontage is on the south. The geometry and zoning constraints result in a building where all sides receive some amount of direct sunlight, with larger exposures being on the east-north-east and west-south-west sides. The greatest opportunity for daylighting was on the west-south-west side—this also presented an overheating risk, which became another design consideration. Glazing areas were kept lower than is typical for an office, and space planning ensured occupants would spend the majority of their time in places with the most daylight. Glass with a low solar heat gain co-efficient (SHGC) was chosen.

The narrow site also had to accommodate parking. A conventional surface parking arrangement with a central drive aisle and two rows of cars would have taken up the entire width. Ramping to an underground parkade would also be awkward and inefficient. Therefore, the design team opted to raise the building and provide surface parking underneath it.

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Further, columns could not interrupt the drive aisle, and zoning setback requirements only allowed enough space for a row of columns on the west side, which could not interrupt access to the parking stalls—a structural challenge in a seismically active area. Hence, it was determined to create three masses. A long, skinny block extending the full height of the four-storey building does most of the seismic heavy lifting, relying on thick, tightly spaced shear walls. The electrical and plumbing services fit within this block, as well as washrooms, elevators, and fire exits.

The main office space is a two-storey block spanning over the drive aisle, providing flexible open offices with the option of being subdivided using temporary partitions for privacy. A stairway in the middle of this block acts as a connecting element, enabling casual conversations in mid-transit. It also doubles as bleacher seating for gatherings of 60 to 70 people. The final, smaller mass on the fourth level houses a multipurpose space for training events and holiday parties and an executive hospitality suite.

Thermal boundary

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In conjunction with developing the massing, the design team also had to determine another PH criteria—thermal boundary. A decision was made to exclude the ground floor, exit stairs, and elevator from the heated envelope. This improved the form factor and avoided thermal bridging and airtightness challenges, any of which could have resulted in missing the required performance targets.

Structure

The building’s geometry presented challenges for seismic design in a high-risk zone. An asymmetric load path and the narrow width available to transfer shear forces to the foundation led to significant forces acting on certain members and connections. This scenario would normally suggest the use of steel or concrete. However, these materials would have resulted in significant thermal bridging challenges—a key consideration for energy performance and the Passive House standard. This influenced the design decision to use cross-laminated timber (CLT) for shear walls and floor diaphragms as a structural solution that could handle the high loads while minimizing the framing’s impact on thermal bridging because of its significantly lower thermal conductivity compared to concrete or steel.

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Additionally, glue-laminated (glulam) timber beams were utilized to handle long spans. Glulam columns were used to support larger point loads, and prefabricated light wood framing was employed where forces were less demanding. The result is a unique hybrid structural system. Wood also provides a biophilic element to the interiors, as the structure is left exposed wherever practical.

Nearly a hundred, unique high-force connections required an intensive design process including the creation of a detailed 3D model of the entire building. The detailed digital model was used as part of the computer numerical control (CNC) fabrication process.

Envelope and sequencing

Only a limited number of local trades have Passive House experience or training, and none of them on a building of this type. Since proper execution of the envelope is essential to achieving a high-performance building, care and attention was given to construction sequencing. The project team determined a simplification of sub-trade scopes would allow for co-ordination and sequencing without the need for every trade to be familiar with PH principals. This was achieved by creating a three-layer system for the exterior walls, each associated with work for a particular sub-contractor: structure, thermal and air barrier, and cladding.

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The structural and cladding sub-trades did not have to do anything different, and the crew with training in high-performance envelopes came between them to do the sensitive work.

The exterior building envelope comprises I-joist Larsen trusses with cellulose insulation and an unsupported, vapour-open weather-resistant barrier (WRB) membrane. This wall system was chosen for its thermal performance and cost effectiveness, and has been used on several other smaller local projects with success. This is the first time this design team (the author is a part of it) used this envelope at a larger scale.

Significant efforts were made during design to reduce envelope penetrations in the build. The final design contains minor wood thermal bridges at key structural locations in the floor as well as façade attachment places. The Passive House Planning Package (PHPP) also confirmed these are insignificant relative to the scale of the building, and do not pose any challenges.

Energy modelling

PHPP is required to track overall certification criteria and quantify the effects of thermal bridges. However, on a project of this scale, it lacked the granularity needed to accurately evaluate heating and cooling loads and overheating risk on a zone-by-zone basis.

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Hence, a third-party hourly analysis program was used to create a dynamic simulation of energy movement and demands within the building (i.e. capable of computing the period of peak heating and cooling demand for separate rooms and zones within the building, and isolating the specific interactions between solar gains, occupancy, internal gains, envelope losses, and air exchanges). A tool of this sophistication is normally used on commercial projects, regardless of Passive House certification, and provides the information needed to make optimized selections of HVAC terminal units (e.g. fan coils) to suit peak zone loads versus plant equipment (e.g. boiler, chiller, variable refrigerant volume [VRV] heat pump) to address dynamic peaks of the building as a whole. It also allows the grouping of zones served by separate sub-systems with unique operating schedules and equipment efficiencies.

HVAC design

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The West Coast has mild winters and summers. Most buildings in this region do not have active cooling. However, the internal gains of an office meant active cooling was part of the design from the start. Summer overheating has been identified as a problem in several residential Passive House buildings, and in this project, the risk was amplified by the internal gains of an office.

Demands for cooling were reduced by selecting efficient lighting systems and strategically placed glazing with solar control. However, even with these measures in place, the preliminary energy model for the project predicted 34 kWh/m²-yr of internal gains. A portion of these gains are useful in the winter months, and in the summer, some of it will be exhausted from the building through the heat recovery ventilation (HRV) system. However, these measures were not enough to negate the need for active cooling.

The thermal demand that must be actively provided for both heating and cooling is met by a VRV system. It was selected for its ability to provide simultaneous heating and cooling in different zones and to internally recover heat as well as its high efficiency cooling operation.

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The availability of Passive House-certified HRV units is limited in Canada, and ones with large enough capacity to meet the ventilation requirements for commercial buildings are rarer. Four units of the largest available size have been installed in Charter’s headquarters. This was an acceptable compromise since the subdivision of the building into different zones allows for better control, and helps avoid over-ventilating areas with intermittent occupancy, especially the fourth-floor event space and hospitality suite.

Lessons learned

When applying Passive House design to a larger, more complex, and locally unique project, a collaborative approach facilitated an understanding of potential challenges, less conventional construction methods, and quality expectations among the construction team, before the design was even issued for build. Instead of viewing the high-performance goal as a burdensome requirement imposed on a bidding proponent potentially unfamiliar with Passive House fundamentals, it became a point of pride that was shared by all team members. This became critical to achieving a high-performance building.

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On a similar note, co-ordination is critical not only during design, but also onsite. Quality training in high-performance building is available for consultants, and tradespersons can also learn some of the essential skills (e.g. how to properly install air barriers) effectively. However, there is no training for general contractors, as it requires changes in approach including sequencing, what to communicate to sub-trades, and other co-ordination issues.

The design team was focused on Passive House criteria throughout the design phase, and that attention seems to have paid off. There have been bumps on the road, but one of the telling lessons learned was energy performance is not the biggest issue. Instead, budget, scheduling, changes requested late, and other problems that can come up in any building project have been the cause of headaches during the construction of the Charter Telecom’s office facility.

Conclusion

This project has demonstrated the Passive House standard can provide value to private commercial building owners. The owner’s main motivation was not sustainability (although that was a factor) but the creation of a quality working environment for staff and upfront investment to achieve lower operating, maintenance, and life-cycle costs.

Regardless of the driving forces behind high-performance building projects, code changes and broader regulatory policies will demand the design-construction industry ramps up its capacity to constantly and cost effectively produce these types of builds. The only known way (without speculative technologies) to limit global warming to below 2 C (35 F) is to reduce demand for energy dramatically, and, in the author’s opinion, a switch to renewables cannot meet demand unless there is less of it. Achieving healthier, comfortable, and higher quality buildings with low-maintenance needs on the scale necessary to limit global warming to below 2 C requires Passive House levels of performance on all new buildings and retrofits.

The Charter building is a milestone in the industry’s road to net-zero energy ready performance. The project’s typology and scale sets it apart from other Passive House builds in the region. The author hopes this project will be a catalyst for high-performance builds to expand into the non-residential market. The success of this project proves massive improvement in energy performance is achievable in a commercial office building located on a challenging site and with builders who did not have previous experience in high-performance buildings.

[11]Graeme Verhulst, Architect AIBC, MRAIC, CPHD, is the co-founder of Waymark Architecture. As keen advocate for advanced building science and the need to move new and existing buildings toward net-zero and beyond, he was an early adopter of Passive House in Canada. He can be reached via e-mail at graeme@waymarkarchitecture.com[12].

Source URL: https://www.constructioncanada.net/passive-house-goes-to-work/

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